1. Field of the Invention
This invention relates generally to a novel method and apparatus for improving a distillation process involving separation of volatile chemical matter or mixture into its ingredient substances. More particularly, the invention relates to a method and apparatus for increasing fractionation capacity and efficiency across existing fractionation trays within an existing distillation column using microdispersers of various designs to increase vapor-liquid interaction across a tray and within the column.
2. Description of Related Art
Fractionation is a unit operation in chemical engineering principle and is employed for separation of a chemical mixture into individual components or compounds due to various chemical compounds having different boiling points under a given system pressure. Fractionation or distillation may be broadly defined as any method by which a vapor or liquid mixture is separated into individual components by vaporization or condensation.
Generally, during distillation, a volume of liquid flows across a vertical stacked series of horizontally mounted tray decks within a cylindrical vessel or distillation column from the top of the column to the bottom. Typically, vapor is introduced into the column through a feed in the lower portion of the column and rises up through small perforations spread over each tray deck. The contact between the vapor phase and the liquid phase of the distillate generates a layer of bubbles or froth. The froth allows the vapor to intimately contact the liquid wherein the vapor phase transfers less volatile matter to the liquid phase. Thus, as the vapor rises up through each tray, the vapor becomes more volatile while the less volatile matter in the liquid phase increases as it moves down on each tray. In turn, the vapor separates from the froth and rises while the liquid separates and is distributed to the tray below. This process occurs many times throughout the column as the vapor rises up and liquid flows down. The distillation trays provide the function of allowing intimate contact or mixing between the vapor and liquid. The trays also separate the vapor and the liquid, thereby allowing the vapor to rise and the liquid to flow in different directions, respectively. Product streams may be drawn at different levels within the column allowing for quick and efficient separation of volatile chemical matter.
In practice, the fractionation of hydrocarbon components within the distillation column occurs continuously across the trays with various streams of vapor and liquid into and out of the column. Revamps or de-bottlenecking of such column of trays are performed on such columns to increase the throughput or capacity of separation between the vapor and liquid phases or improving the fractionation efficiency. Several types of revamps include adding new separation zones such as adding a packed material, changing the distillation area by changing an inlet region such as a downcomer, and/or adding multiple downcomers within the column. In order to begin such revamp, the distillation column must be shut down and all hydrocarbon processing is stopped leading to loss of processing time and ultimately, loss of profits.
U.S. Pat. No. 4,604,247 issued to G. Chen et al. describes a revamp utilizing structure of a packed material and method. Folded structured packing is added to replace the trays within the column. However, typical packing is complex or bulky in either a structured or random form which requires removal some or all of the trays to optimally install the packed material. This increases the cost and time of installation.
Another type of distillation apparatus revamp is a multiple downcomer arrangement, which attempts to increase the effective active area of a tray deck. U.S. Pat. No. 5,547,617 issued to A. Lee, et al. describes a revamp structure, which replaces in part or in whole of the internal tray structure of the distillation column. The entire tray deck structures are removed such that new trays with multiple downcomers in a U-shaped pattern are installed in place of the original trays. Thus, a large amount of additional material is needed to construct and manufacture each new tray with the supporting downcomer and active bridge baffle.
U.S. Pat. No. 6,003,847 issued to A. Lee et al. illustrates a modified downcomer structure with an activated inlet portion. However, the typical construction and revamp discards the original internal structures within the distillation column. Totally new components are assembled within the column thereby increasing the waste material and time involved in the field installation.
In U.S. Pat. No. 6,095,504 issued to Heldwein et al., a modified support structure for revamping distillation column internals is disclosed. A single ring support at a lower bottom tray deck is configured to support upper tray decks in order to speed installation. Likewise, this apparatus does not reuse the internal structures thereby increasing waste material and manufacturing costs.
The details of revamping a distillation column are also disclosed in U.S. Pat. No. 6,113,079 to Urbanski. An adjustable circumference fractionation tray includes slideable decking plates, which aid in the installation of the new tray decks. However, additional bolting and new sliding tray deck structures must be manufactured and installed leading to increased down time and potential problems with the adjustable tray deck surfaces.
Accordingly, there is a need for a revamp method and apparatus which increases the capacity and efficiency of a distillation column with existing fractionation trays. It would be desirable that inactive areas of the tray deck are xe2x80x9cactivatedxe2x80x9d to provide an additional increase in the vapor-liquid interaction in the inactive area. The revamp and conversion apparatus should be easy and simple to manufacture and install while retaining enough durability for use in the vapor and liquid environment of hydrocarbon processing. The revamp apparatus should also be easy to install to substantially reduce the labor cost and provide time savings during critical installations. There is a need for a kit for performing the revamp during a regular maintenance cycle with minimal shutdown time while still increasing the efficiency across the existing fractionation trays.
A method and apparatus for increase fractionation capacity and efficiency of chemical compounds within a preexisting distillation column is disclosed. The apparatus upgrades a preexisting distillation column with a vertically oriented vessel having at least one preexisting horizontally oriented fractionation tray deck mounted inside the vessel. The preexisting fractionation tray deck separates lighter vapor rising from below the tray deck and heavier liquid flowing across the top of the tray deck surface. The tray deck has a multiplicity of openings where the lighter vapor flows through to mix with the liquid to form froth. According to the present invention, a conversion microdisperser is configured to attach through one of the openings in the tray deck to disperse the vapor stream through the liquid flow to enhance the fractionation of volatile hydrocarbons and/or other chemicals in greater capacity and with greater efficiency.
The microdisperser may be a microdispersion valve or an individual bubble promoter. The microdispersion valve preferably is easy to install within the tray deck by means of a quick connect leg means or conventional legs and has a perforated deflection means which further helps to separate the vapor and liquid in a more efficient manner. The microdisperser bubble promoter is a box-like structure, which is configured to attach through an individual tray deck opening and may cover a portion of the adjacent tray deck. The microdisperser bubble promoter has perforations, slots or tabs to further separate and/or direct the vapor stream through the liquid flow. The microdisperser valves or bubble promoters may be round, square, rectangular or any other suitable vapor dispersing shape.
One embodiment of the present invention may be characterized as a microdisperser, which attaches through two or more openings in the tray deck. The microdisperser may be configured to be a continuous apparatus, which lies over the entire inlet portion in a one-piece structure. A downcomer panel may be situated above the inlet section in a segmented, conical or round shape, which would correspond to a respective continuous microdisperser shape.
Another embodiment of the present invention is a microdisperser bubble promoter that spans over an inactive area with two vapor openings in the tray deck separating the inactive area and providing the attachment area for the microdisperser. The inactive area may be over a major or minor tray support beam or the inactive area may be located at the edge of the distillation column vessel wall. The individual microdisperser will preferably direct vapor stream from the inactive zone through liquid flow such that fractionation capacity and efficiency is increased.
A method of using the apparatus for the subject fluid flow and enhancing interaction of fluids is provided. Conventional fractionation trays have inactive zones or areas and stagnant liquid back flow located at the inactive zones. The inactive areas may be located at an inlet portion under a downcomer, which is subject to a high rate of liquid flow. Microdisperser valves and/or bubble promoters may be placed at the inactive areas to promote vapor-liquid interaction over the existing fractionation tray. A specific microdisperser is selected and placed in the inactive area to preferentially direct the stream of vapor through the flow of liquid.
A kit for realizing the subject improvement of preexisting trays for fractionation columns is disclosed with instructions and a diagram for placing the microdispersers throughout the existing tray deck and hardware and tools for attaching the microdispersers to the tray deck.
In general, one advantage of the present invention is to provide an efficiency and capacity upgrade to an existing distillation column with preexisting trays.
Another advantage is reducing the cost and time of distillation column modernization during a routine maintenance while preserving the tray decks or panels of existing trays. Thus, process plant downtime is greatly reduced, thereby maximizing operating profits.
A further advantage of the present invention is to provide an economical way to convert the existing trays to highest performance possible without resorting to a full or partial replacement of the existing trays with new tower internal structures according to various embodiments of the prior art within the field of mass transfer art. Many parts may be recycled and reused thus saving time, resources, and the environment.
Yet another advantage of the present invention is to provide an apparatus of the above character, which reduces the cost of energy and material to fabricate the components for the practice of the present invention. Reduction of the present invention to practice will result in inexpensive, easy and quick modernization of the existing process plants with columns of fractionation trays to achieve substantial energy savings, improving product purity and increase in plant capacity.
The accompanying drawings, which are incorporated in, and form a part of this specification, illustrate embodiments of the invention and, together with the following description, serve to explain the principles of the invention.